The Complement System
The complement system, an essential component of the innate immune system, plays a critical role as a defense mechanism against invading pathogens, primes adaptive immune responses, and helps remove immune complexes and apoptotic cells. Three different pathways comprise the complement system: the classical pathway, the lectin pathway and alternative pathway. C1q and mannose-binding lectin (MBL) are the structurally related recognition molecules of the classical and lectin pathways, respectively. Whereas IgM or clustered IgG serve as the principal ligands for C1q, MBL recognizes polysaccharides such as mannan. Ligand binding by C1q and MBL results in the sequential activation of C4 and C2 to form the classical and lectin pathway C3-convertase. In contrast, alternative pathway activation does not require a recognition molecule, but can amplify C3 activation initiated by the classical or lectin pathways. Activation of any of these three pathways results in the formation of inflammatory mediators (C3a and C5a) and the membrane attack complex (MAC), which causes cellular lysis.
While the complement system plays a critical role in many protective immune functions, complement activation is a significant mediator of tissue damage in a wide range of autoimmune and inflammatory disease processes. (Ricklin and Lambris, “Complement-targeted therapeutics.” Nat Biotechnol 2007; 25(11):1265-75).
A need exists for complement regulators. On the one hand, the complement system is a vital host defense against pathogenic organisms. On the other hand, its unchecked activation can cause devastating host cell damage. Currently, despite the known morbidity and mortality associated with complement dysregulation in many disease processes, including autoimmune diseases such as systemic lupus erythematosus, myasthenia gravis, and multiple sclerosis, only two anti-complement therapies have recently been approved for use in humans: 1) purified, human C1-Inhibitor licensed for use in patients suffering from hereditary angioedema (HAE) and 2) eculizumab (Soliris™), a humanized, long-acting monoclonal antibody against C5 used in the treatment of paroxysmal nocturnal hemoglobinuria (PNH). Both PNH and HAE are orphan diseases in which very few people are afflicted. Currently, no complement regulators are approved for the more common disease processes in which dysregulated complement activation plays a pivotal role. Dysregulated complement activation can play a role in both chronic disease indications and acute disease indications. Acute disease indications include, amongst others, acute intravascular hemolytic transfusion reaction (AIHTR), birth asphyxia, hypoxic ischemic encephalopathy, ischemia-reperfusion injury (IRI) in myocardial infarct, coronary artery bypass surgery and stroke, and solid organ transplantation rejection.
Astrovirus Coat Protein
The Astroviridae constitute a family of non-enveloped, icosahedral viruses with a single-stranded, messenger-sense RNA genome. These viruses are a significant cause of gastroenteritis in humans as well as other diseases in other animal species. It is estimated that they cause an estimated 2-17% of children's diarrheal illness worldwide.
The Astrovirus coat protein (“CP”) reduces the activity of the complement system, suggesting that the ‘active’ portion of the protein may have clinical utility in decreasing tissue damage from complement-mediated diseases. The wild type coat protein (“WT CP”) purified from human astrovirus type 1 (HAstV-1) can bind C1q and MBL, and regulates both classical and lectin pathway activation (Bonaparte et al., 2008. J. Virol. 82, 817-827; Hair et al., 2010. Molec. Immunol. 47, 792-798). This property is analogous to the properties described for human neutrophil peptide-1 (HNP-1)(Van Den Berg et al., 1998. Blood. 92, 3898-3903; Groeneveld et al., 2007. Molec. Immunol. 44, 3608-3614). The HAstV-1 coat protein is a 787 amino acid molecule that has been expressed from a recombinant baculovirus construct and then purified (Bonaparte et al., 2008. J. Virol. 82, 817-827).
Developing peptide compounds to inhibit classical, lectin and alternative pathways of the complement system is needed, as each of these three pathways have been demonstrated to contribute to numerous autoimmune and inflammatory disease processes. Specific blockade of classical and lectin pathways is particularly needed, as both of these pathways have been implicated in ischemia reperfusion-induced injury in many animal models. Humans with alternative pathway deficiencies suffer severe bacterial infections. Thus, a functional alternative pathway is essential for immune surveillance against invading pathogens.
Microbial and Bacterial Infections
Many microorganisms are resistant to currently available antibiotics. Current antibiotics are derived from other microbial organisms that bacteria have competed against for space and energy over many years, which has led to rapid and predictable emergence of resistance. Some of the most pathogenic bacteria to humans are Pseudomonas aeruginosa, Staphylococcus aureus, MRSA, and carbapenemase-resistant enterobacteriacea (CREs) such as Klebsiella pneumonia. Pseudomonas aeruginosa and Staphylococcus aureus are also major pathogens in cystic fibrosis lungs. Gardnerella is a Gram variable, anaerobic coccobacillus that is a common cause of bacterial vaginosis. Gardnerella also causes complement activation and inflammation, which causes the symptoms of bacterial vaginosis and increases the risk of HIV transmission by disrupting normal barrier defenses in the vagina. There is a need for treatments for bacterial vaginosis that kill the causative organism and block inflammation. There is also a need for novel antimicrobial compounds given the increasing resistance to conventional antibiotics.
Herpes simplex virus 1 (HSV-1) and herpes simplex virus 2 (HSV-2) are viruses responsible for causing herpes. Infection with HSV-1 can happen from general interactions such as eating from the same utensils, sharing lip balm, or kissing. The virus is highly contagious, and it is possible to get genital herpes from HSV-1 if the individual has had cold sores and performed sexual activities during that time. Similarly, HSV-2 is also highly contagious. HSV-2 is contracted through forms of sexual contact with a person who has HSV-2. It is estimated that around 20 percent of sexually active adults within the United States have been infected with HSV-2, according to the American Academy of Dermatology (AAD). While HSV-2 infections are spread by coming into contact with a herpes sore, the AAD reports that most people get HSV-1 from an infected person who is asymptomatic, or does not have sores. Current treatments like acyclovir for HSV-1 or HSV-2 may not be fully efficacious. Thus, there is a need for anti-viral treatments for HSV-1 and HSV-2 that are more effective against viruses.
Lactobacillus Growth
Lactobacillus is a genus of bacteria that contains over 180 species. Multiple Lactobacillus species are often administered together as a single probiotic agent. In combination, various Lactobacillus species have been known to help individuals with irritable bowel syndrome, prevent necrotizing enterocolitis, and other neonatal infections. Because of its many health benefits, there is a need for compounds that can stimulate growth of Lactobacillus species.
Cystic Fibrosis
Cystic fibrosis (CF) is a genetic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Patients with CF produce unusually thick, sticky mucus that clogs the lungs and leads to life-threatening lung infections, and obstructs the pancreas and stops natural enzymes from helping the body break down food and absorb vital nutrients. CF is characterized by a cycle of small airway obstruction, infection with bacterial pathogens, e.g., P. aeruginosa, Staphylococcus aureus (including methicillin-resistant S. aureus (MRSA), Burkholderia cepacia, and inflammatory lung damage. Complement-mediated inflammation may be a major contributor to inflammatory lung damage in CF. Treatment of CF includes a regular treatment routine to maintain lung health and good nutrition. Other treatments for CF include airway clearance every day to help loosen and clear thick mucus that can build up in the lungs, inhaled medicines, including antibiotics, to help keep the airways clear, and pancreatic enzyme supplements to improve absorption of vital nutrients. There is a need for both anti-inflammatory and anti-microbial treatments for CF.
Hemolytic Transfusion Reactions
Blood transfusions can be life-saving, but can also carry the risk of a variety of reactions, some of which are potentially life-threatening, such as acute intravascular hemolytic transfusion reactions (AIHTRs). AIHTR is estimated to occur in one-fifth of total transfusions. Individuals receiving frequent blood transfusions will develop alloantibodies and autoantibodies to red blood cell (RBC) antigens over time, making cross-matching increasingly difficult and thus increasing the risk of AIHTR. Current transfusion safe-guards include “typing”, “antibody screening”, as well as “cross matching.” While these measures have made transfusions safer, transfusion reactions still occur. AIHTR occurs when host antibodies bind to the transfused erythrocytes, initiating classical complement pathway activation, which leads to the generation of the inflammatory mediators C3a and C5a, as well as C3b opsonization and hemolysis of the transfused cells via the membrane attack complex (MAC). To date, only one case has been reported describing clinical intervention of an AIHTR by inhibiting generation of the complement anaphylatoxins C3a and C5a. No specific interventions for these reactions exist; current management of the reaction is supportive in nature. While existing safeguards make ABO incompatibility rare in the developed world, individuals with sickle cell disease and severe thalassemias requiring frequent transfusions are at increased risk for transfusion reactions due to the accumulation of antibodies against minor antigenic determinates on erythrocytes. Neonatal ABO incompatibility in newborns can lead to jaundice, and, in severe cases, kernicterus. No blood banking organization or transfusion medicine practice has a method to directly evaluate risk for complement-mediated red blood cell lysis between donor and recipient. There is currently no effective medical intervention for ATRs except for stopping the transfusion. Diagnostic tools, prophylactic treatments to prevent AIHTR, and rescue treatments during an AIHTR are needed.
Birth Asphyxia
Birth asphyxia is a medical condition resulting from deprivation of oxygen to a newborn that causes brain damage. Hypoxic ischemic encephalopathy (HIE) is a condition that occurs when the entire brain is deprived of an adequate oxygen supply, but the deprivation is not total. HIE is most often associated with birth asphyxia. Reperfusion injury is the tissue damage caused when blood supply returns to a tissue after a period of ischemia or lack of oxygen. The absence of oxygen and nutrients from blood during the ischemic period creates a condition in which the restoration of circulation results in inflammation and oxidative damage through the induction of oxidative stress rather than restoration of normal function. Complement activation is instrumental in the development of ischemia-reperfusion injuries such as neonatal HIE. Therapeutic hypothermia (HT), the current standard of care for HIE, offers only an 11% reduction in death or disability. Published data has shown that HT paradoxically increases pro-inflammatory complement activation, which potentially limits its benefit. There is a need for treatments for HIE and birth asphyxia that regulate complement and have neuroprotective effects.
Autoimmune Hemolytic Anemia
Autoimmune hemolytic anemia (AIHA) is a disease that occurs when antibodies directed against a person's own red blood cells cause them to burst, leading to insufficient plasma concentration. AIHA is most commonly caused by IgG and IgM. IgM is a potent activator of the classical complement pathway. Thus, AIHA is characterized by complement mediated lysis of red blood cells. Thus, there is a need for therapies directed at the complement system to treat AIHA.
It would be desirable to develop peptide compounds that can regulate complement activation and can be used therapeutically to prevent and treat complement-mediated diseases, such as inflammatory and autoimmune diseases. It would also be desirable to develop peptide compounds that treat acute diseases and conditions such as acute intravascular hemolytic transfusion reaction (AIHTR), birth asphyxia, autoimmune hemolytic anemia, viral infections, and bacterial infections, amongst others. It would also be desirable to develop peptide compounds that treat cystic fibrosis.